Preheat the oven to 375°F (190°C).
Cut pears into small cubes (you don't have to peel them), set aside.
Prepare a muffin pan (standard size) and line it with 12 paper liners. Spray the liners with a non-stick baking spray (optional).
Add the butter, eggs, yogurt, vanilla, baking powder, baking soda, salt, cardamom, cinnamon, and both types of sugar into a large bowl. Whisk until well combined.
Add the flour, fold in with a spatula until almost combined.
Add the pears and walnuts, fold in with a spatula until evenly distributed and there are no streaks of flour visible. Don’t overmix the batter.
Divide the batter evenly between 12 muffin liners.
Make the topping: stir brown sugar with cinnamon and chopped walnuts. Sprinkle the topping over the muffin batter.
Bake for about 25 minutes or until a wooden skewer/cake tester comes out clean.
Place on a cooling rack to cool slightly and enjoy!